The purpose of the present study was investigate the effects of laser irradiation on control of inflammtion in human dental pulp. Human dental pulp (HDP) cells were obtained from the unerupted teeth extracted from a young patient in the course of orthodontic treatment. HDP cells were treated with peptidoglycans of Lactobacillus casei or LPS of Porphiromonas endodontalis as inflammatory model, Then laser (The low-enaergy GA-Al-As diode laser a (Panalas-1000, Matsushita, wavelength 830 nm, max power 600 mw) beem was delivered by an optical fiber 0.6 mm in diameter, with the distance from the tip of the fiber to the cell layer being 55 cm for 5 min (3.75J/cm2). The production of IL-1β, IL-6 and prostaglandin and activity of tisue type plsminogen activator was significantly decreased by laser irradiation to compared with non-irradiation. The expression of tmRNA IL-1β, IL-6, Cox2 and tPA was decreased. It is suggested that laser irradiation decreases progression of pulpitis. Then to investigate the effects of laser irradiation in dental pulp tissue. The occlusal exposures in rats moler were made by using handpiese (bur size : 1/2 round). The continious drilling was intermitted until the pulp chamber was exposed. 2 days after pulp exposure, all of the rats were deeply re-anesthetized with ether, and the maxillary and mandibular bone with surrounding tissues were dissected. The sections were prepared HE stain, and observed. However, the findings were not detected the effects of laser irradiation. In fituer, it seems that the pulpal tissue exporsed and laser irradiated were observed using in situ hybridization in order toclarify of detail inframmatory reactions of dental pulp.